1. Field of the Invention
The present invention relates generally to integrated circuit (IC) components, such as semiconductor dice, and more particularly to interposers for mounting semiconductor dice on substrates.
2. Disclosure Information
In conventional flip-chip mounting processes, a semiconductor IC die 50 (see FIG. 1A) is typically "bumped", a process wherein thick metal layers (e.g., 25-100 microns) of gold or solder 24 are metallurgically bonded to the IC die's aluminum bond pads 54. The bumped IC die is then flipped "upside down" with the bumps 24 facing downward against mating mounting pads 72 on a substrate 70 (e.g., a printed circuit board), whereupon solder reflow (for solder bumps) or diffusion bonding (for gold bumps) is used to bond the bumps with their respective substrate mounting pads, as illustrated in FIG. 1B.
Because IC dies have traditionally been wire-bonded to leadframes and then encased in polymer or ceramic packages (as in DIPs, QFPs, etc.), the bond pads on an IC die are typically arranged about the periphery of the die's bonding surface (i.e., near the outer edge or perimeter of the die). This presents no problem for using flip-chip bonding so long as the die size is large, and/or the number of bond pads is low (thereby permitting the use of large pads); however, as the die size shrinks and/or the number of bond pads increases, the bond pads must be made smaller and/or more closely spaced (i.e., finer pitched), which makes registration and bonding of the bonding pads to the mounting pads much more difficult.
One way of addressing this problem has been to distribute the bond pads 24 across most of the entire face of the bonding surface (FIG. 2), rather than limiting the bond pads to the conventional perimeter locations (FIG. 1A). However, when the bond pads are brought inward from their typical perimeter locations toward the center of the bonding surface, they lie atop the transistors and other delicate solid state devices 52 located thereat, separated only by a thin passivation layer 56. This presents a problem because the heat and/or pressure required to melt or diffuse the bumps 24 (in order to form metallurgical bonds between the bond pads and mounting pads) often damages the adjacent/underlying transistors and IC devices 56. This problem has therefore limited flip-chip bonding, practically speaking, to the use of relatively low-temperature, low-pressure solder reflow processing with perimeter-only bond pad locations; but, as mentioned above, this places serious limits on the number of bond pads that can be used.
It would be desirable, therefore, to provide a way of enabling the use of a higher number of bond pads, without the aforementioned potential of damaging the delicate transistors and other IC devices.